I had a machine that was locked up when I got it. The bushings that the center rod passed through, the thing that turned the bobbin case, were all corroded. Not really rusted, just stuck. I had to loosen some screws, set screws, etc and finally got it apart. Is it possible, when you got it unstuck, you disengaged one of those (or more) set screws? check to see if the rod spins while you move the hand wheel. That rod should spin the bobbin holder. (Forgive me, I really don't know all the technical terms)